1. Field of the Invention
The present invention relates to a technique for printing dots on the surface of a print medium using dot printing heads, and in particular to a technique for efficiently printing large and small images.
2. Description of the Related Art
Printers which eject ink from the nozzles of printing heads have recently come to enjoy broad popularity as computer output devices. Such printers with numerous nozzles can print dots for rapid printing of large images by using these numerous nozzles at once. These techniques are disclosed, for example, in Japanese Unexamined Patent Application (Kokai) 2001-232806.
FIG. 19 illustrates an example of interlace printing. Interlace printing is sometimes employed in the above printers in order to achieve high quality printing. During interlace printing, various parts of the printed image Img are printed with various nozzles For example, the parts at the top edge of the image Img are printed by nozzles #10 and #11 near the upstream end (bottom end in FIG. 19) in the sub-scanning direction SS among the nozzle rows, and are printed by nozzle #1 near the downstream end (top end in FIG. 19) of the sub-scanning direction SS. The parts near the bottom end of the image Img are printed by nozzle #12 near the upstream end in the nozzle rows, and are printed by nozzles #2 and #3 near the downstream end of the nozzle rows.
During interlace printing, the image Img begins to be printed, as illustrated in FIG. 19, at a position where nozzles #10 and #11 near the upstream end (bottom end in FIG. 19) of the nozzle rows face the top end of the image Img. The image Img ends to be printed at a position where nozzles #3 and #4 near the downstream end (top end in FIG. 19) of the nozzle rows face the top end of the image Img.
Meanwhile, at the start of interlace printing, the main scan lines cannot be printed without gaps in the area where the downstream side nozzles (nozzles #1, #2, etc.) print. Thus, in a case where the next image Img begins to be printed after the first image Img (indicated by the aggregate of solid circles in FIG. 19) has been printed, and the printing of the next image begins from the specific relative position of the printing head and print medium where the first image Img has been completed, the next image Img is printed at the position indicated by the dashed line in FIG. 19.
Accordingly, when images are printed multiple times on continuous paper, the images have had to be printed at certain intervals. Thus, in the case of smaller printed images, the images are not printed proportionately to the surface area of the printing paper that can be used to print the images, resulting in a greater waste of printing paper area.
An object of the invention is to provide a technique that allows large images to be rapidly printed and smaller images to be more efficiently printed on a printing medium, such as paper, in order to address the above drawbacks in the related art.